# What is Time dilatation: Definition and 31 Discussions

In physics and relativity, time dilation is the difference in the elapsed time as measured by two clocks. It is either due to a relative velocity between them (special relativistic "kinetic" time dilation) or to a difference in gravitational potential between their locations (general relativistic gravitational time dilation). When unspecified, "time dilation" usually refers to the effect due to velocity.
After compensating for varying signal delays due to the changing distance between an observer and a moving clock (i.e. Doppler effect), the observer will measure the moving clock as ticking slower than a clock that is at rest in the observer's own reference frame. In addition, a clock that is close to a massive body (and which therefore is at lower gravitational potential) will record less elapsed time than a clock situated further from the said massive body (and which is at a higher gravitational potential).
These predictions of the theory of relativity have been repeatedly confirmed by experiment, and they are of practical concern, for instance in the operation of satellite navigation systems such as GPS and Galileo. Time dilation has also been the subject of science fiction works.

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1. ### B How to measure time in reference frame with clock?

I considered example of time dilation with light clock. I have a question about measuring time in reference frame with clock. If we know that clock move from A to B in the reference frame with clock then what time of motion is measured in this reference frame? (In non-moving reference frame...
2. ### I The Theoretical Minimum: Length Contraction and Time Dilation

Hello, My name is Dave and I'm a physics major at UIUC. It looks like I will be taking the special relativity course (phys 225) this fall. I've always been fascinated by the theory so I decided to get a head start with Lenny and Art's perspective on it. My first head-scratching moment came in...
3. ### I GPS clock synchronization in ECI frame

Hi, starting from this old thread GPS clock synchronization I've a doubt about the physical process employed to synchronize clocks bolted on GPS system satellites. We said that clock synchronization is frame dependent. In other words we must select a coordinate chart (aka reference frame) that...
4. ### Rocket moving away from the Earth

I first began to identify the various events in the problem. I call the rocket ##S'## and the Earth ##S##. Sending signal Tail signal reflection Head signal reflection Tail signal return Head signal return For the Earth I know that: ##t_4 = T## ##t_5 = T + \Delta T## Since the two events...
5. ### Time dilatation between straight and curved lines in Minkowsi space

Summary:: Special relativity - 2 astronauts syncronize their clocks and moves in different paths at different velocities, which clocks is left behind? and why? Hi everyone, i have the following problem and I'm not understanding if my strategy to solve it is correct: Two astronauts synchronize...
6. ### I Why does time dilation only affect one of the twins?

I am more confused by the theory of relativity as I start thinking about it. I have a question and it might sound silly but please, correct me if I am wrong. Suppose, A and B are twins where A is at the Earth, and B is moving on a spacecraft at a speed near to the speed of light. In this...
7. ### Longitude contraction / time dilatation

I get the same values for both observers, which is not nice I think.
8. ### I Gravitational time dilatation and curved spacetime - follow up

Hi, starting from this very interesting thread I'm still a bit confused about the conclusions. The main point, as far as I can understand, is all about conditions for a quadrilateral to be considered a parallelogram. My first basic doubt is: the concept of 'parallel' applies just to geodesic...
9. ### I Sending Signal from Planet Near Gargantua: A Thought Experiment

The other day my friend asked me a really interesting question regarding the scene from interstellar where they go down to Miller's planet, where every hour on this planet is 7 years of Earth time. He asked me if they were to send a signal to the spaceship where Romilly was, what would happen...
10. ### B Reference frame symmetry in Special Relativity

Hello, I have a couple of questions related to reference frames in Special Relativity. Let's consider a rocket that is inertially moving towards a star with a relative velocity 0.9c. I'd like to look at this example from both the rocket's and the star's perspectives. In the reference frame of...
11. ### Is This the Proper Frame for Your Needs?

The attempt is above
12. ### B Satellite Clocks: General & Special Relativity Time Variations

Something that crossed my mind recently; I know that satellites have to adjust their clock due to their relativistic time variations in relation to us. I was wondering do they adjust their times in accordance to general relativity or special relativity or both? Or is their speed so insignificant...
13. ### I Time dilatation thought experiment

Hello everyone, this is my first post on this forum, I am a new member and the other day was pondering on a question related to the passage of time. So, I have the following thought experiment: Suppose there is the following setup: We have two small toy cars, identical, each capable of...
14. ### I Deriving Lorentz from time dilation and length contraction

Is it possible to derive the Lorentz transformation from time dilation and length contraction? If so, how should I start? I know how to derive it while considering 4 scenarios finding values of A, B,D,E in x'=Ax+Bt t'=Dx+Et and the transformation is: x'=(x-vt)/sqrt(1-v^2/c^2)...
15. ### SR - Time dilation, space-time diagram, and radio signals

Homework Statement P.S.: I'm not sure if it is allowed to ask multi-part questions. Two equally old sisters Alice and Barbara leave Earth simultaneously in opposite directions. The following velocities and distances have been measured in the Earth system. Alice travels with a speed of ##v_A =...
16. ### Finding the relativistic speed of a spacecraft

Homework Statement If a spacecraft is traveling to a star which is located at a distance of 1 lightyear and it would take the spacecraft 1 year to reach the star in its own frame, how fast would the spacecraft actually fly? Also, how long would the journey take for an observer on Earth...
17. ### I Relativistic mass increase (simple or not)

Hi, I have yet another question in the field of the special relativity theory. I always thought that the derivation of the relativistic mass is trivial. But I discovered that there is some complexity due to the transverse and longitudinal relativistic mass derivation. I saw a thread where...
18. ### Time Dilation in the same frame of referance?

Homework Statement A rocket ship is accelerating through space. Clocks P and Q are at opposite ends of the ship. An astronaut inside the rocket ship is beside clock P and can also observe clock Q. What does the astronaut observe about the passage of time for these clocks? Justify your answer...
19. ### I Communicating at Near-Light Speed - Time Dilation

So, I've been wondering: how would time dilation affect communications? For the sake of visualisation, imagine the Flash is running at 99% the speed of light in a circle around a fixed position. There's a building in this position, and inside this building are his friends. Due to time dilation...
20. ### Time dilation and acceleration due to gravity

If acceleration and acceleration due to gravity is equivalent , then by equivalence principle if we accelerate through universe at the equal to acceleration due to gravity near black hole , does that mean that there will be same time dilation while we accelerate in the universe like when we...
21. ### A rocket ship leaves earth at a speed 0.6c. When a clock....

Homework Statement A rocket ship leaves Earth at 0.6c. The clock of the rocket says 1hr has elapsed. (a.) According to the earth clock, when was the signal SENT? (b.) According to the earth clock, how long after the rocket left did the signal arrive BACK on earth? (c.) According to the rocket...
22. ### What must be one's speed, relative to a frame S, in order....

... in order that one's clocks will lose: (a) 1 second per day as observed from S? (b) 1 minute per day as observed from S? I was referencing this:( http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html#c2 ) hyperphysics page but I still can't seem to understand what I need to do to...
23. ### Lorentz Transformations or Dilation/Contraction?

I'm doing a class on special relativity and when doing some problems, I'm never sure whether I should be using the Lorentz transformations (Eg. x' = γ(x-vt) or t'=γ(t- (v/c^2)x)) or the Time dilation and Length contraction equations to find t or x! Can anyone explain if there's any way of...
24. ### Analysis of the physics in Interstellar

So I recently watched the new movie Interstellar, and I've been inspired to do some more general relativity. At one point in the movie they mention that 1 hour on a planet orbiting a black hole is 7 years back on Earth, and so I decided my first project would be to figure out exactly how close...
25. ### Time Dilatation: The Twins Paradox

We’ve all seen this little fellas up there. Two brothers, twins, in their 60’s. And they decide that one of them is going to take a trip into space, let’s say for a year, at 99% the speed of light. The other brother stays there, waiting for his twin to return, and looking at the light clock that...
26. ### Why are time dilatation & length contraction infinite at light speed?

Considering that speed of light is constant and finite, then why are the time dilatation and length contraction infinite to a frame of reference moving at the speed of light? We know that a moving frame of reference experiments time dilatation and length contraction from the point of view of a...
27. ### Twins paradox and time dilatation

I have already read about the twins paradox a lot of times, but what puzzles me is that how the Universe would "now" what twin had to be younger since, if the spaceship travels at high speed in relation to Earth, the planet would move the same with the ship as reference.
28. ### Gravitational time dilatation

Here http://curious.astro.cornell.edu/question.php?number=278 I see the following: Do I understand right that mentioning slower time passage at the bottom of the tower here is slightly inappropriate? Red-shifting of the light here is totally accounted for by photons loosing some energy...
29. ### Redshift and time dilatation of Hawking radiation

Micro black holes should in principle be observable by emitting Hawking radiation. However, as this takes place extremely close to the event horizon, shouldn't one expect then extreme redshifting (z = 1/(1-Rs/R)^-1/2 -1, Rs = Schwarzschildradius, R = Radius of Emission) and time dilatation? In...
30. ### Time dilatation and 'now slices'

i read brian greene's book 'the fabric of the cosmos' a long while ago, and i remember being surprised by the notion that one's 'now slice' of reality can angle toward the past OR the future of someone else's. (toward past if moving away, toward future in moving toward someone who is...
31. ### Is the gravitational time dilatation a real effect?

Some people explain that gravitational time dilatation is just photons redshifting due to work they are doing against gravitational field while escaping from it, but I heard that the delay of the clock on the probe after passing near Jupiter was observed.